What is Momentum?
Momentum measures how hard it is to stop a moving object — it depends on both how much mass is moving and how fast. It's a vector quantity central to collisions, sports, and rocket science.
Momentum is the product of an object's mass and velocity: p = m·v, measured in kg·m/s. A heavier or faster object has more momentum.
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Step-by-step worked examples
A 1200 kg car moves at 20 m/s. Find its momentum.
p = m·v p = 1200 × 20 p = 24000 kg·m/s
A 0.145 kg baseball is thrown at 40 m/s. Find its momentum.
p = m·v p = 0.145 × 40 p = 5.8 kg·m/s
A cyclist and bike have a combined mass of 75 kg moving at 8 m/s. Find the momentum.
p = m·v p = 75 × 8 p = 600 kg·m/s
Flashcards
Quick quiz
Q1.A 5 kg object moves at 4 m/s. What is its momentum?
Q2.Which is the correct unit of momentum?
Q3.Two objects have equal mass. Which has more momentum?
Q4.In a closed system with no external force, total momentum is…
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Common mistakes
Treating momentum as a scalar with no direction. — Correct: Momentum is a vector — direction matters, especially in collisions.
Confusing momentum with kinetic energy. — Correct: Momentum is m·v (linear in v); kinetic energy is ½m·v² (quadratic in v).
Assuming momentum is conserved even with an external force. — Correct: Momentum is only conserved when the net external force is zero.
Forgetting to convert units before calculating. — Correct: Always use SI units — kg for mass, m/s for velocity — before multiplying.
FAQ
What is momentum?
Momentum is the quantity of motion an object has, given by p = m·v, where m is mass and v is velocity.
What is the formula for momentum?
p = m·v — momentum equals mass times velocity, measured in kg·m/s.
How do you calculate momentum with real examples?
Multiply the object's mass (kg) by its velocity (m/s). For example, a 1000 kg car at 15 m/s has p = 1000 × 15 = 15000 kg·m/s.
Why is momentum important in physics?
It's conserved in collisions and explosions, making it essential for analyzing car crashes, sports impacts, and rocket propulsion.